Methods and systems for self-servo-writing including writing positioning and timing bursts at different track pitches

ABSTRACT

Methods and systems for self-servowriting a data storage medium are disclosed, including servoing to propagation bursts of a propagation pattern located in tracks other than an immediately preceding track. Reference levels used to position a recording head are accordingly kept in a usable dynamic range necessary to keep servo track spacing constant across the medium. The methods and systems are disclosed in connection with a rotary actuator having spaced read and write heads. Similar methods are disclosed for writing trigger or timing bursts of the propagation pattern.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.08/654,950, filed May 29, 1996, now U.S. Pat. No. 5,757,574.

This application is related to the following commonly owned U.S. patentapplications:

Ser. No. 08/028,044 of T. Chainer et al. filed on Mar. 8, 1993 entitled"A Method and System for Writing a Servo-Pattern on a Storage Medium;"

Ser. No. 08/348,773 of T. Chainer et al., filed on Dec. 1, 1994 entitled"Improvements in Self-Servowriting Timing Pattern Generation;" and

Ser. No. 08/349,028 of E. Yarmchuk et al., filed on Dec. 2, 1994entitled "Radial Self-Propagation Pattern Generation for Disk FileServowriting."

Each of these applications is hereby incorporated by reference herein inits entirety.

FIELD OF THE INVENTION

This invention relates generally to storage devices for computers. Moreparticularly, it relates to a disk drive apparatus, and to a method forwriting servo information therein.

BACKGROUND OF THE INVENTION

Increased levels of storage capacity in floppy and hard disk drives area direct result of the higher track densities possible with voice-coiland other types of servo positioners. Previously, low track density diskdrives were able to achieve satisfactory head positioning with leadscrewand stepper motor mechanisms. However, when track densities are so greatthat the mechanical error of a leadscrew-stepper motor combination issignificant compared to track-to-track spacing, an embeddedservo-pattern is needed so that the position of the head can bedetermined from the signals it reads.

Conventional hard disk manufacturing techniques often include writingservo-patterns on the media of a head disk assembly (HDA) with aspecialized servowriter instrument. Laser positioning feedback is usedin such instruments to read the actual physical position of a recordinghead used to write the servo-patterns. Unfortunately, it is becomingmore and more difficult for such servowriters to invade the internalenvironment of an HDA for servowriting because the HDAs themselves areexceedingly small and depend on their in-place covers and castings forproper operation. Some HDAs are the size and thickness of a plasticcredit card. At such levels of microminiaturization, traditionalservowriting methods are inadequate.

Conventional signals of servo-patterns typically comprise short burstsof a constant frequency signal, very precisely located offset from adata track's center line, on either side. The bursts are generally, butnot required to be, located in a trajectory within a track. The burstsare written in a sector header area, and can be used to find the centerline of a track. Staying on center is required during both reading andwriting. Since there can be sixty, or even more, sectors per track, thatsame number of servo-pattern areas must be dispersed around a datatrack. These servo-pattern areas allow a head to follow a track centerline around a disk, even when the track is out of round, as can occurwith spindle wobble, disk slip and/or thermal expansion. As technologyadvances provide smaller disk drives, and increased track densities, theplacement of servo-patterns must also be proportionately more accurate.

Servo-patterns are conventionally written by dedicated, externalservowriting equipment, and typically involve the use of large graniteblocks to support the disk drive and quiet outside vibration effects. Anauxiliary clock head is inserted onto the surface of the recording diskand is used to write a reference timing pattern. An external head/armpositioner with a very accurate lead screw and a laser displacementmeasurement device for positional feedback is used to preciselydetermine transducer location and is the basis for burst placement andspacing of bursts in successive tracks. The servowriter requires a cleanroom environment, as the disk and heads will be exposed to theenvironment to allow the access of the external head and actuator.

U.S. Pat. No. 4,414,589 to Oliver et al. describes servowriting whereinoptimum track spacing is determined by positioning one of the movingread/write heads at a first limit stop in the range of travel of thepositioning means. A first reference burst is then written with themoving head. A predetermined reduction number or percentage of amplitudereduction X %, is then chosen that is empirically related to the desiredaverage track density. The first reference burst is then read with themoving head. The moving head is then displaced away from the first limitstop until the amplitude of the first reference burst is reduced to X %of its original amplitude. A second reference burst is then written withthe moving head and the moving head is then displaced again in the samedirection until the amplitude of the second reference burst is reducedto X % of its original value. The process is continued, writingsuccessive reference bursts located in successive tracks and displacingthe moving head by an amount sufficient to reduce the amplitude to X %of its original value, until the disk is filled with reference bursts intracks (i.e., a propagation pattern). The number of reference bursts sowritten is counted and the process is stopped when a second limit stopin the range of travel of the positioning means is encountered. Knowingthe number of tracks written and the length of travel of the movinghead, the average track density is checked to insure that it is within apredetermined range of the desired average track density. If the averagetrack density is high, the disk is erased, the X % value is lowered andthe process is repeated. If the average track density is low, the diskis erased, the X % value is increased and the process is repeated. Ifthe average track density is within the predetermined range of thedesired average track density, the desired reduction rate X %, for agiven average track density, has been determined and the servowriter maythen proceed to the servowriting steps, using the collection ofreference bursts written as a propagation pattern. This technique cannotaccommodate changes in reference levels which may be required across thedisk surface.

The process of servowriting using only the internal recording transducerand product actuator, (one form of self-servowriting) is thus generallyknown to involve a somewhat rigid application of three largely distinctsubprocesses: writing and reading magnetic bursts to provide precisetiming; positioning the recording transducer at a sequence of radiallocations using the variation in readback signal amplitude frompropagation bursts as a sensitive position transducer; and writing theactual product servo-pattern at the times and radial locations definedby the first two subprocesses. Again, such techniques currently sufferfrom exposure to changing conditions across the disk surface, and, inaddition, to manufacturing tolerances in the HDAs themselves.

What is required are systems and methods for self-servowriting which aremore flexible and which overcome the deficiencies of the presently knownself-servowriting techniques.

SUMMARY OF THE INVENTION

Briefly summarized, the present invention, in one aspect, is a methodand system for writing propagation bursts in a self-servowriting system.The system has a storage medium with a plurality of tracks for holdingbursts therein. The method and system include servoing to a firstpropagation burst located in a first track in the plurality of tracks,and writing a second propagation burst in a second track of theplurality of tracks while servoing to the first propagation burst. Thefirst track does not immediately precede the second track.

The first track may succeed the second track, in which case the methodand system may further include servoing to a third propagation burstlocated in a third track of the plurality of tracks, and writing thefirst propagation burst in the first track while servoing to the thirdpropagation burst, wherein the third track precedes the second track.

The first track may precede the second track (i.e., there is at leastone track between the first track and the second track) in which casethe first track may be the penultimate preceding track relative to thesecond track.

The method and system may also include servoing to a plurality ofpropagation bursts, including the first propagation burst, located inrespective tracks of the plurality of tracks. In this case, the writingmay include writing the second propagation burst while servoing to theplurality of propagation bursts. Further, the servoing may includederiving a function from signals received from the plurality ofpropagation bursts, and the function may be a weighted averagecalculated from the signals.

In another aspect, the present invention is a method and system forwriting product servo-pattern bursts in a self-servowriting systemhaving a storage medium with a plurality of tracks for holding burststherein. The method and system include writing a first productservo-pattern burst in a first track of the plurality of tracks. Themethod and system further include writing a second sequential productservo-pattern burst in a second track of the plurality of tracks whileservoing to a third propagation burst located in a third track. Thethird track is located intermediate the first track and the secondtrack. There may be a plurality of propagation bursts located inrespective tracks of multiple tracks of the plurality of tracks. In thiscase, the multiple tracks include the third track and are locatedintermediate the first track and the second track in which thesequential product servo-pattern bursts are written.

In yet another aspect, the above-described positioning sequences may becombined in a method and system for keeping a reference signal level ina usable dynamic range. The reference signal level is used to position awrite head while writing a propagation pattern on a surface of a storagemedium of a self-servowriting system. The method and system includeusing a first positioning sequence for reading and writing a firstportion of propagation bursts of the propagation pattern over a firstregion of the surface. The method and system further include using asecond, different positioning sequence for reading and writing a secondportion of propagation bursts of the propagation pattern over a secondregion of the surface. The reference signal level is thereby kept in theusable dynamic range for positioning said write head while writing thefirst and second portions of the propagation pattern.

In still another aspect, the present invention includes a method forwriting timing and positioning bursts of a propagation pattern in aself-servowriting system. The system may have a storage medium with aplurality of tracks for holding bursts therein. The method and systeminclude writing a plurality of successive propagation bursts comprisinga portion of the propagation pattern in first respective tracksseparated by a first track pitch. Further, a plurality of successivetiming bursts are written comprising said portion of the propagationpattern in second respective tracks of the plurality of tracks. Thesecond respective tracks are separated by a track pitch different thanthe first track pitch. At least one of the first respective tracks maycomprise at least one of the second respective tracks.

The above-described methods and systems are especially useful in aself-servowriting storage system having a circular medium with aplurality of radial tracks therein, and wherein a rotary actuator isused to self-servowrite the medium.

By employing the methods and systems of the present invention, changesin reference levels can be accommodated across the medium surface,thereby compensating for changing self-servowriting conditions acrossthe disk surface, including compensating for manufacturing tolerances inspaced read and write heads and the skew angle of a rotary actuator.

DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the present invention is particularlypointed out and distinctly claimed in the concluding portion of thespecification. The invention, however, both as to organization andmethod of practice, together with further objects and advantagesthereof, may best be understood by reference to the following detaileddescription of the invention and the accompanying drawings in which:

FIG. 1a depicts two positions of a magneto-resistive read and writeelement pair possible in a rotary actuator system;

FIG. 1b depicts read element amplitude changes from an on-track tooff-track position;

FIG. 2a depicts a manufactured offset possible between the centers ofread and write elements;

FIG. 2b depicts displacing a read element just enough to reduce the readback amplitude to a reference level maximum;

FIG. 2c depicts displacing the read element just enough to reduce theread back amplitude to a reference level minimum;

FIG. 3a depicts a typical skew angle for a typical rotary actuatoracross a disk surface;

FIG. 3b depicts the resulting offset between the read and write elementsfor the rotary actuator of FIG. 3a;

FIGS. 3c and 3d depict changes in the minimum and maximum move distancesacross the disk surface;

FIG. 3e depicts the usable dynamic range of a reference level for anexemplary desired track spacing (servo track spacing=1/2 data trackspacing) across the disk surface;

FIG. 4 depicts a first positioning sequence according to the principlesof the present invention;

FIG. 5 depicts a second positioning sequence according to the principlesof the present invention;

FIG. 6 depicts a third positioning sequence according to the principlesof the present invention;

FIG. 7 depicts a fourth positioning sequence according to the principlesof the present invention; and

FIGS. 8a-b depict timing pattern and propagation pattern generationaccording to the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The inventors of the present invention have discovered that theshortcomings of the previously described techniques are especiallyproblematic if considered in connection with the use of modernmagneto-resistive heads which use separate magneto-resistive read andinductive write heads. For recording heads in which the read and writeelements are physically separate, the dynamic range of radialdisplacement is a function of the read and write widths and the relativeoffset of the read to write element. Further, when used in combinationwith rotary actuators, the offset also becomes a function of the angularposition of the actuator. Unfortunately, for certain combinations of theabove parameters, the radial displacement required may not be achievablewithin the usable dynamic range of a reference level used to positionthe actuator. The prior techniques do not address separate read andwrite elements, on rotary actuators, and the resulting dynamic rangelimit. This invention overcomes these limitations by proposingalternative propagation positioning techniques.

Self-servowriting, when used herein, connotes generally using the mediumitself, and propagation patterns thereon, to position the head duringwriting of the product servo-pattern. Although in preferred embodimentsthe same head system is used to write the propagation patterns, productservo-patterns, and read and write data on the medium; otherself-servowriting systems may include separate head systems for writingthe propagation patterns, product servo-patterns, and reading andwriting data on the medium.

Magneto-resistive recording heads used in current disk drive designs mayhave separate read and write elements or heads as shown in FIG. 1a. Theread 105 and write 100 elements typically have different widths and arephysically separated by a distance D 120. When these heads are used incombination with modern rotary actuators in exemplary positions 115 and110 respectively, the read and write offset 125 changes due to the skewangle 130 of the head to track resulting from the angular rotation ofthe actuator and the physical distance D 120 between the elements. Theoffset is given by:

    Offset=D sin(Θ)

In the propagation of bursts, the read element is servoed to the edge ofan amplitude burst. A position signal is obtained by measuring thenormalized read head amplitude. The head is servoed to a predeterminedpercentage (i.e., "reference level") of the on-track amplitude whichdisplaces the head radially with respect to the propagation burstcenters. As shown in FIG. 1b the normalized read element amplitudechanges approximately linearly from 1 when on-track to 0 when the readelement is completely off-track. In practice there are limits on theminimum and maximum reference levels required to provide a positionsignal for the servo system which we will refer to as Reference LevelMaximum 150 and Reference Level Minimum 160. The radial displacement (inthis embodiment measured along the trajectory of the actuator)corresponding to a change in amplitude is a function of the differencein the write element width 170 and the read element width 180 and alsothe offset 125 between the centers of the read and write elements asshown in FIG. 1a. In addition, there may also be an offset between thewrite and read elements built into the head design at the time ofmanufacture, and/or other manufacturing tolerances which aggravate theself-servowrite problems discussed above.

In the above-identified U.S. patent application entitled "RADIALSELF-PROPAGATION PATTERN GENERATION FOR DISK FILE SERVOWRITING," atechnique is disclosed to adjust the reference level across the disksurface to maintain proper track spacing. However, that application doesnot address any techniques to overcome the absolute maximum and minimumlevels discussed herein.

There are two ranges of motion which can be calculated from the dynamicrange of the on-track amplitude referred to respectively as theMinimumMove and the MaximumMove.

The case of propagation of the pattern from inside diameter ("ID") tooutside diameter ("OD") is described, but similar equations can bewritten from the OD to ID. In either case, the tracks in which thepropagation patterns and servo-patterns are written can be considered tobe arranged successively relative to this general direction ofpropagation across the disk surface. The offset is defined as positiveif the read element center is displaced towards the OD relative to thecenter of the write element. The MinimumMove corresponds to the minimumdisplacement the read head will undergo corresponding to the minimumchange in read signal amplitude from the on-track value. As shown inFIG. 2a, a dual element head may have a manufactured offset 210. TheMinimumMove distance shown in FIG. 2b corresponds to displacing the readelement 105 just enough to reduce the readback amplitude to theReference Level Maximum to allow servoing of the head to the edge of thepropagation burst track. As shown in FIG. 2b the MinimumMove distance isgiven by ##EQU1## where W_(write) is the write width, W_(read) is theread width, and (F_(min)) W_(read) (215) is the fraction of the readelement width which is displaced beyond the edge of the writtenamplitude burst.

The MaximumMove as shown in FIG. 2c corresponds to the maximumdisplacement the head will undergo corresponding to reducing the headreadback amplitude to the Reference Level Minimum. This can similarly beshown to be given by: ##EQU2## where (F_(max)) W_(read) (220) is thefraction of the read element width which is displaced.

For linear actuators the offset is a constant and therefore theMinimumMove and MaximumMove distances are fixed for the entire databand. However, in the case of rotary actuators, the offset is a functionof radial position, therefore the Minimum and MaximumMove distance willdepend on the radial location of the head. The skew angle for a typicalrotatory actuator shown in FIG. 3a has a change of skew angle of -5 to17 degrees when the rotary actuator moves from the ID to the OD datatrack over the surface. (Assuming a write width of 3.1 μm and a readwidth of 2.3 μm and a write-to-read element distance of 3.6 μm.) Thisresults in an offset of the read and write elements which is plotted inFIG. 3b and shows a shift in the read/write offset of approximately 1.3microns from the ID to OD.

The MinimumMove distance is shown in FIG. 3c, and the MaximumMovedistance is shown in FIG. 3d for the case of a Reference Level Maximumof 0.9 and a Reference Level Minimum of 0.3. As shown in FIG. 3e, forthe case of a minimum servo track pitch equal to 1/2 of the data trackpitch the head would not be able to displace that distance over theentire data radius.

The present invention expands the range of accessible servo trackpitches using one, or alternatively a combination of, the followingsequences as described below:

Product servo track spacing is less than MinimumMove

In the case when the MinimumMove distance exceeds the servo track pitch,several positioning sequences are disclosed to overcome this limit.These three sequences all have in common the feature that bursts outsidean immediately preceding track are used while writing. These sequencescan be considered either spatial or temporal sequences.

a. Sequence #1:

When the MinimumMove distance exceeds the servo track spacing, headpropagation is attained by combinations of larger forward and smallerbackward moving steps as shown in FIG. 4. Each step of FIG. 4 having adotted line shows the self-servowriting process at a point where thehead is servoing to a first propagation burst and writing a secondpropagation burst. A burst, as used herein, broadly connotes any form ofphysical manifestation, on the disk surface, used to carry informationor to position the head (e.g., transition, pulse, pulse train, etc.) Theproduct servo-pattern is shown at the left as a continuous vertical lineof data that has been stitched together from repeated writes at the samesector location, for illustrative simplicity. The propagation bursts areshown in the middle with the labels, "n", "n+1", . . . indicating thesequence of propagation bursts at successive radial locations. Tracks200 are shown corresponding to bursts n and n-3; the overlapping tracksn-1 and n-2 are not shown. (Tracks are merely regions on the mediumwhich generally accommodate a trajectory of bursts.) The collection oftracks 200_(n-3) . . . 200_(n) are referred to herein as a plurality ofsuccessive tracks on the medium, and when the terms "preceding" and"succeeding" are used herein, they connote the physical relationship ofthe tracks unless otherwise explicitly indicated. Track 200_(n-1) is"penultimate" to track 200_(n+1), and track 200_(n) is between orintermediate these two tracks.

The radial location of the read (105) and write (100) elements is shownat the right, with the dotted line indicating the edge of the referencepropagation burst used to generate a succeeding propagation burst. InStep 1, the propagation burst "n" has been written, but the range ofmotion exceeds the minimum servo track space and therefore thepropagation burst n+2 320 is next written (Step 2) by servoing to theoutside edge of burst n. In Step 3 the missing propagation burst n+1 330is written by reversing direction and servoing to the opposite edge ofburst n+2. The corresponding product servo-pattern burst n+1 may also bewritten at this time. This allows the servo-pattern to be written at asmaller step size than the propagation step size. Step 4 illustrateswriting the product servo-pattern burst n+2. The process is thenrepeated. (It will be understood that the particular sequence of writingthe product servo-pattern bursts is generally independent of thesequence in which the corresponding propagation bursts are written. Inthis example, servo-pattern bursts are written sequentially as wouldoccur in a phase encoded pattern. The propagation bursts, however, arenot written sequentially.) Thus, when writing bursts n+2, and n+1, therecording head servos on a burst other than that located in animmediately preceding track.

b. Sequence #2:

An alternative sequence to solve this limitation is shown in FIG. 5. Inthis case, when writing propagation burst n+1 420, the recording headcan servo on a preceding propagation burst (i.e., in track 200_(n-1))other than that located in the immediately preceding track (i.e.,200_(n)). As shown in FIG. 5 the head servos to propagation burst n-1440 (in track 200_(n-1)), when writing burst n+1 (in track 200_(n+1))420 to allow an increased range of motion. Track 200_(n+1) is the trackpenultimate to track 200_(n+1).

C. Sequence #3:

An alternative sequence is shown in FIG. 6. In this case, several burstsn, n-1, n-2 and n-3 are weighted to define a new radial location forpropagation burst n+1. An exemplary weighting function is ##EQU3## wherea=weighting coefficients, and S=the burst amplitude or an averageamplitude for a burst track. This method may be employed in a mannersimilar to Sequence #1 in which writing the servo-pattern is delayed byone or more steps of propagation pattern writing with subsequentreversing of servo direction.

It will be understood that writing the servo-pattern may be postponeduntil after the entire propagation pattern has been written across theentire disk surface.

For Sequence #3, the servo-pattern can be written in a separate processof stepping across the disk using the weighted amplitude burst readingsof the propagation pattern to servo to any desired servo track spacing.

One alternative method to overcome changes in reference level requiredto maintain a fixed propagation burst spacing across the medium, is tofix the reference level to a predetermined value (e.g. 50%) and writepropagation burst tracks across the disk surface. The fixed propagationreference level will result in a variation in the propagation bursttrack spacing while maintaining a constant reference level within ausable range.

Upon completion of writing propagation burst tracks across the entiredisk surface, the recording head is servoed to radial positions derivedfrom the weighted values of the propagation burst amplitudes on morethan one track: ##EQU4## wherein S is the average burst amplitude for apropagation burst track and a are the weighting coefficients for thattrack. Note that since the propagation burst tracks are already written,either or both preceding and succeeding burst tracks can be used in thiscalculation, or any combination thereof.

Using the calculated servo reference levels, the radial position of thehead can be determined and product servo bursts can be written at anydesired track spacing. As the propagation burst track spacing isvarying, the weighting coefficients will vary in a predetermined mannerand generally as a function of radial location across the disk tomaintain the desired product servo burst track spacing.

Product servo track spacing is greater than MaximumMove

In the case when the MaximumMove distance is less than the servo trackpitch, a sequence is shown in FIG. 7. The product servo-pattern iswritten every other propagation step on step n 720 and step n+2 740, butnot on intermediate steps n+1 730. Therefore, propagation bursts arewritten in tracks intermediate the tracks where product servo-patternbursts are located. This process can obviously be extended to every Nthstep N greater than 2.

According to the principles of the present invention, the implementationof these propagation techniques can be selectively applied in the systemonly when required in certain regions of the surface during theservowriting process to improve the dynamic range. In one embodiment,the techniques associated with FIGS. 4 and 7 are selectively applied tocompensate for spacing less than MinimumMove and greater thanMaximumMove corresponding to different areas of operation of the headsover the surface. This variation of techniques can take place in anautomated fashion in which the reference level is monitored and thetechniques adjusted, or it can take place with a priori knowledge ofexact techniques needed over respective portions of the disk, dependingon the known skew angles, manufacturing tolerances, offsets, etc.

Timing Pattern Propagation

The methods of providing radial pattern propagation bursts weredescribed above. The self-servowrite process includes both the writingof radial patterns and timing or trigger patterns. The propagation oftrigger patterns requires a reference level minimum which depends on thesignal to noise ratio of the trigger pattern. In certain cases thisminimum may be different than the radial requirements for a desiredservo-pattern track pitch.

In order to solve this problem, we add one or more additional triggerpropagation steps between each servo-pattern write. For example, if thepropagation patterns were to be written at 1/2 track steps, and theamplitude was too low at this pitch, a trigger propagation pitch of 1/4or 1/6 or even 1/8 of a track might be chosen. Servo bursts would onlybe written at the appropriate steps. As shown in FIG. 8a, the timingpatterns 800, 805, 810, 815, 820 are written at the same step size asthe radial amplitude propagation patterns of 1/2 track. In FIG. 8b, thetiming patterns 820, 825, 830, 835, 840 are written at 1/4 step whilethe radial propagation bursts are written at 1/2 step. The triggerpropagation only steps could be accompanied by radial propagation stepsor simply generated by using a sequence of different reference levelsfrom a single radial propagation step.

Disclosed herein are methods and systems for self-servowriting whereinthe reference levels used to create a propagation pattern are keptwithin a usable dynamic range. In addition to alleviating the need for acomplex mechanical and/or optical positioning system to establishservo-patterns on the recording surfaces, the methods and systems solvethe problems associated with maximum and minimum reference levels due tomanufacturing tolerances, spaced read/write heads, and/or the angularmotion of rotary actuators over a recording surface.

It will be understood that the present invention may be applicable tothe writing of patterns on any type of storage medium that moves in arepetitive fashion. While such motion may constitute successiverotations of the medium described above, it may also constitute anyrepetitive or continuous motion including rectilinear and reciprocatingmotion. Thus, any propagation pattern may be provided over an area of astorage medium using the self propagation principles described herein.

While the invention has been described in detail herein in accordancewith certain preferred embodiments thereof, many modifications andchanges therein may be affected by those skilled in the art.Accordingly, it is intended by the following claims to cover all suchmodifications and changes as fall within the true spirit and scope ofthe invention.

What is claimed is:
 1. A method for writing timing and positioningbursts of a propagation pattern in a self-servowriting system having astorage medium with a plurality of tracks for holding bursts therein,said method comprising:writing a plurality of successive propagationbursts comprising a portion of the propagation pattern in firstrespective tracks of the plurality of tracks, said first respectivetracks separated by a first track pitch; and writing a plurality ofsuccessive timing bursts comprising said portion of the propagationpattern in second respective tracks of the plurality of tracks, saidsecond respective tracks separated by a second track pitch differentthan said first track pitch.
 2. The method of claim 1, wherein at leastone of the first respective tracks overlays at least in part at leastone of the second respective tracks.
 3. A storage medium readable by amachine and tangibly embodying a product servo-pattern written byservoing to the propagation pattern written according to claim
 1. 4. Asystem for writing timing and positioning bursts of a propagationpattern in a self-servowriting system having a storage medium with aplurality of tracks for holding bursts therein, said systemcomprising:means for writing a plurality of successive propagationbursts comprising a portion of the propagation pattern in firstrespective tracks of the plurality of tracks, said first respectivetracks separated by a first track pitch; and means for writing aplurality of successive timing bursts comprising said portion of thepropagation pattern in second respective tracks of the plurality oftracks, said second respective tracks separated by a second track pitchdifferent than said first track pitch.
 5. The system of claim 4, whereinat least one of the first respective tracks overlays at least in part atleast one of the second respective tracks.